The present invention relates to a circuitry including an electronic control circuit for controlling the control coils of preferably a number of servo devices in a hydraulic system.
According to the prior art the pump delivery rate has to be adjusted in response to the delivery rates which are required by the consumers in a hydraulic system. So-called load sensing systems are known including means to sense the load pressure which occurs at the highest loaded consumer which load pressure signal is supplied to a pump control valve for adjusting the pump delivery rate required. The pump control valve thus adjusts the pump delivery rate of the pump in response to the flow rate through the consumer. However, when the maximum delivery rate is reached or when the delivery rate cannot be further increased by some reasons and when one of the consumers signalizes a requirement for an increased flow rate the hydraulic system changes in a state of under-supply and the highest loaded consumer comes to a stop. In order to avoid this the prior art provided means to restrict the flow rate to the consumers, for example by switching off a consumer or by a proportional decrease of flow rate to all consumers.
German P 26 51 325 discloses a hydraulic system in which the directional valves controlling the consumers are hydraulically controlled via pilot valves. In the state of undersupply the pilot pressure acting on the directional valves may be decreased to reduce the flow rate through the consumers. German P 35 32 816 discloses a hydraulic system in which a pressure compensating valve each cooperates with each directional valve for a load-independent control of the flow rates. In this system a hydraulic signal is generated in the state of under-supply which signal acts on the pressure compensating valves for an adjustment in the closing direction. In addition to systems above referred to providing a load pressure responsive hydraulic control German P 35 46 336 teaches to reduce the supply voltage delivered to electrical control means controlling the directional valves of the consumers when the pump delivery rate is not any more sufficient to supply the required volume. In this system the desired values for the flow rates to the consumers are defined by electrical signals which are summed up and compared with a limit signal corresponding to the maximum pump delivery rate. The control thus takes place in response to the desired values of the flow rates.
The object of the present invention is to reduce the expenditure for actuating the servo devices of the hydraulic system when the pump power is not sufficient and to ensure in a particularly simple manner that the flow rates to the consumers are adjusted to the pump capacity available. The term "pump power" or "pump capacity" is to be understood as defining a delivery rate of the pump or an exaggerated pressure or a state of operation in which the driving means of the pump reaches a limit. A further object is to adjust the pump delivery rate to the volume the consumers require.